(a) Field of the Invention
The present invention relates to an electroconductive transparent adhesive composition, and an electroconductive transparent adhesive produced using the composition. The electroconductive transparent adhesive can be used as an adhesive in various electrical and electronic applications such as displays, touch screens, touch lenses, electronic devices, and electrical electrodes, and can also be used as a medical tape, a wrapping tape, or a masking tape.
(b) Description of the Related Art
Adhesives are used in a wide variety of applications such as sheets, films, labels and tapes due to their easy usability, and the materials to be adhered also include a wide variety of materials such as organic materials, metallic materials and inorganic materials. Recently, the range of applications is gradually extending over displays, touch screens, touch panels, touch lenses, electronic devices, electrical electrodes, and LED lightings, where high functionality in various properties, and high durability and reliability against moisture, corrosion and temperature are required. Particularly, in regard to the application of adhesives, for the purpose of weight reduction and miniaturization in electronic industries, adhesives have been applied to the surface packaging on printed circuit boards, adhesion of liquid crystal display devices, and adhesion of magnetic materials to video/audio films, and the like.
Compounds are used in the adhesives as described above can be classified, on the basis of components, into rubber-based adhesives, silicone-based adhesives, acrylic adhesives, and the like. The rubber-based adhesives have poor heat resistance and weather resistance, exhibit severe fluctuation in fluidity along with temperature change, and also have a disadvantage that a large amount of residue remains on the material to be adhered; therefore, recently, an investigation on adhesives containing synthetic rubbers such as SBR (styrene-butadiene rubber), BR (butyl rubber), NBR (nitrile-butadiene rubber) and TPR (thermoplastic rubber) as main components is in active progress.
The silicone-based adhesives are adhesives that have been most recently developed, but they are disadvantageous in that the use of the adhesives is limited only to special applications, and the adhesives are expensive and, in particular, cannot be used for general purposes.
Regarding the rubber-based and silicone-based adhesives, research has already seen significant progress; however, active investigations on the acrylic adhesives are only now being conducted. The acrylic adhesives have excellent weather resistance and oil resistance that the rubber-based or silicone-based adhesives do not have, and adhesives suitable for the purpose can be relatively easily produced by inducing polar groups in an arbitrary polymer molecule in consideration of the polarity of the material to be adhered. Furthermore, the acrylic adhesives have the same characteristics as those of other general adhesive from the viewpoint that the molecular structure, terminal group or branching property of the polymer and the like affect the adhesive, and there is selectivity even in view of the form, such as a solvent type adhesive, an emulsion type adhesive, or a solvent-free type adhesive. Therefore, the acrylic adhesives have currently secured a position in the pertinent art.
On the other hand, transparent adhesives are used for interlaminar bonding by which components are stacked up when a liquid crystal display device (LCD) is produced, or for the attachment of a touch screen to a mobile telephone. The optical transparent adhesives described above belong to an organic adhesive-synthetic-resin-thermoplastic-acrylic system. Optical transparent adhesives that are currently commercially available have a light transmittance of 97% or higher so that the optical transparent adhesives increase resistance to humidity, temperature and corrosion as in the case of glass, and the flection of the surface is as small as about 1% and uniform as compared with existing double-sided tapes so that the optical transparent adhesives increase the clarity of screens while exhibiting good adhesiveness. Such functional adhesives employ polymer materials and are more flexible than conventional metallic materials or the like, and are thus applicable to the fields of adhesive films, sheets and tapes for flexible displays, touch screens, touch panels, touch lenses and the like.
Furthermore, regarding an electroconductive adhesive, for example, US Patent Application Publication No. 2009-0311502 A1 suggest a method for producing an electroconductive adhesive by mixing a non-tertiary alcohol having 4 to 14 carbon atoms and an acrylic acid ester having an alkyl group, with electroconductive flakes. Furthermore, U.S. Pat. No. 7,494,708 B1 reports a method for producing a pressure-sensitive adhesive by polymerizing a block copolymer from a (meth)acrylate monomer. In this case, bulk resistance decreases as the proportion occupied by the electroconductive adhesive increases, and the bulk resistance decreases to approximately 10−3 Ωcm. However, since metals such as silver, gold and copper are used as the conductive flakes, transmittance is almost undetectable, and since the particles are heavy, the flakes settle down and cause the adhesive to be further non-uniform.
Due to the lack of electrical conductivity or due to the opaque characteristics, conventional transparent adhesives or electroconductive adhesives are restricted in the applications where transparency is required, such as in displays and touch screens. Also, since most of electroconductive adhesives are formed from expensive metal particles, the electroconductive adhesives are highly expensive. Therefore, there is a demand for the development of an electroconductive transparent adhesive has advantages of low production cost, excellent adhesive power, excellent transmittance and excellent electrical conductivity.